This invention relates to metal halide lamps, and more particularly, to rapid restrike metal halide lamps and method of operating such lamp which are particularly suitable for sport stadium lighting applications.
Standard metal halide lamps having an arc tube disposed therein and containing constituents, typically require a relatively long duration such as 10 to 15 minutes, in which the power may be reapplied to the arc tube to initiate or restrike its arc condition following any power interruption to the lamp which caused the extinction of arc conditions of such a previously operating lamp. Such metal halide lamps suffer a disadvantage in certain lighting systems such as those employed in sport stadiums. For example, if the lighting system of the sports stadium experiences a power outage, it is desired that the initiation or restrike of the arc tube be attempted within a few seconds, rather than 10 to 15 minutes, so that the sporting activity being performed can be resumed within a relatively short time and observed by those people at the stadium and also those that may be viewing the event on television.
Metal halide lamps that allow for this restrike condition require a starting or ignition waveform of a relatively high voltage at a relatively high current level from external circuitry in order to initiate a desired ionization condition of the constituents within the arc tube. To accommodate this type of starting or restrike waveform, the metal halide lamp itself must be provided with sufficient insulation and spacing between the conductive members within the lamp carrying this restrike waveform so that arcing therebetween does not occur within the lamp itself. It is desired that a metal halide lamp be provided which accepts this type of starting waveform without the need to resort to excessive insulation within the lamp so as to safeguard against any related arcing condition in the lamp.
The metal halide lamp having the rapid restrike capability should also take into account the requirements of the external circuity supplying the lamp. The metal halide lamp should present to such external circuitry a load having a relatively low stray capacitance so that such circuitry may be able to develop the desired starting waveforms at a periodic repetition rate without experiencing undue transmission losses.
Accordingly, it is an object of the present invention to provide a rapid restrike metal halide lamp that accepts a starting waveform of a relatively high voltage at a relatively high current level from external circuitry without the need of excessive insulation within the lamp and also present a relatively low stray capacitance load to the external circuitry.